Pollinators + plants = food. Right? The domesticated honeybee, along with a handful of wild bee species, is in decline. But 75 percent of the 115 major crop species grown around the world rely on pollinators to give us that food. This equation is woefully out of balance.

Pollinator-dependent crops make up only a fraction of total agricultural revenues, but that’s because the nine priciest crops, which together comprise half of global agriculture as measured by revenue, can become pollinated by wind, or can pollinate themselves. But the economic value of agriculture is only one way to understand the value of different crops. Another is the value of the different crops to human health and nutrition.

Pollinator-dependent crops, despite forming only contributing a small amount of revenue, contribute a great deal to dietary diversity. While pollinator-independent grains can provide most of the calories we need, argues Stanford University researcher Rebecca Chaplin-Kramer this week in Proceedings of the Royal Society B, nutritional requirements require a more diverse set of crops. In fact, most of our micronutrients come from crops that rely on bees and other pollinators. If pollinators continue to decline, while we may be able to rely on other crops for sustenance, our nutrition will surely suffer.

In some parts of the world, it already has. That’s because agricultural practices and pollinator dependence are not uniformly distributed across the globe. Chaplin-Kramer and colleagues from the Natural Capital Project, a collaborative research effort between Stanford’s Woods Institute for the Environment, the University of Minnesota’s Institute on the Environment, The Nature Conservancy, and the World Wildlife Fund, set out to determine the overlap between pollinator dependence and malnutrition, in order to identify geographic areas where future research on pollination services will be most critical.

The researchers focused on three micronutrients critical for human health, and which enter the human diet primarily via plants: vitamin A, iron, and folate. Vitamin A deficiency can result in visual impairment or blindness, and increases the risk of death from common infections. Iron deficiency is linked with pregnancy complications, and has been associated with one out of every five maternal deaths. Folate deficiencies are implicated in neurodevelopmental disorders like spina bifida.

Micronutrient deficiencies, they discovered, are three times more likely to occur in geographical areas that are most dependent on pollinators, like India, Southeast Asia, and central and southern Africa. On the other hand, the US, Europe, China, and Japan are most economically dependent on pollinators. That economic dependence on pollinators is localized to developed countries while nutritional dependence on pollinators is found in poorer areas, suggests that impoverished nations will face greater health risks due to the agricultural disruptions that will occur, and are occurring already, because of pollinator declines.

The particular crops from which these micronutrients are derived also vary from region to region. Pumpkin, melon, and mango are important for vitamin A, but they’re outpaced by okra in India, tropical fruits like guava in India and Thailand, apricot and sour cherry in Iran, plum in Romania, and peach in Mexico.

One perhaps obvious solution to this problem is to shift agricultural production from pollinator-dependent crops to ones that are independent of pollinators. However, a full transition would require significant changes not just to agricultural practices, but also to eating habits. And culinary diversity is one of the most interesting parts of human culture.

Reverting from pumpkin to sweet potato as a source of vitamin A in India or Thailand, for example, is possible since the two crops are similar both in flavor and texture. However, Chaplin-Kramer points out, dietary preferences are deeply culturally ingrained. Moreover, even for crops that are designated as pollinator-independent – because the part we eat does not rely on pollination – it could still be necessary for seed production. The parts of sweet potato, carrot, lettuce, and spinach that we eat do not require pollination, but all require it to reproduce. It is just not as simple as reverting from fruits to leaves.

In addition, various fruits give you more bang for your buck: pumpkins, tropical fruits, and melons all contain either two or all three of vitamin A, iron, and folate; pollinator independent crops are not typically as nutritionally dense.

The truth is there is no single solution to a problem of this scope. Instead, the researchers hope that their analysis will provide an impetus for conducting more research in parts of the world that are traditionally neglected by academic research. “In regions that are both highly pollinator dependent and nutritionally vulnerable, local ecological studies should be undertaken to quantify the ecosystem service provided by wild and managed pollinators, and to estimate the value of natural or semi-natural habitat to maintaining that service,” they say. The best, most intensively studied areas for understanding pollinators are in California, New Jersey, Costa Rica, and Europe. Meanwhile, the places that are in dire need of research are known for chronic malnutrition, like India, Africa, and Southeast Asia.

Policymakers will have to determine whether it is the quantity, quality, or monetary value of crop production that is most important to consider when identifying regions most at need of assistance when it comes to pollinator decline. However, “it is clear that these different metrics lead to different conclusions about focal regions for further study, and until now human health considerations have not been driving the choice of study location,” the researchers argue. When it comes to setting conservation priorities, “while carbon sequestration and water-related services often receive a great deal of attention…more localized services like pollination deserve special consideration,” they add. – Jason G. Goldman | 19 September 2014